For many years it has been known that during use at least the positive battery plates within a lead-sulphuric acid battery will become longer from the chemical reactions going on within the battery. In an effort to overcome any problems relating to such plate growth battery manufacturers have in the past provided additional space beneath plates. In some prior art batteries the plates themselves were hung within a heavy walled container which could support their weight. Accordingly, covers had always been held tightly in place so that no motion between the battery jar or the terminal posts was permitted. Any plate growth would be absorbed on the bottom and if problems developed the battery would be discarded or would be completely broken down and repaired.
In recent years the thickness of battery jars has been reduced to reduce the size and weight of batteries. Thus, it is desirable to have the battery plates rest on grids which in turn are directly mounted on the bottom of the jar. Also, one barrier to the use of polyproplyene covers heat welded to polyproplyene battery jars has been the growth of the positive posts which has become a greater problem now that the plates essentially rest on the bottom. In such a circumstance, it is most important to provide some means of absorbing or allowing plate growth to occur any way that will not force the cover from the jar thereby ruining the battery for its intended purpose.
Another known attempt to find a solution to positive plate growth problems involved the use of a cover having wells in the shape of inverted truncated cones. An opening was provided in the center of the flat bottom portion and a rubber grommet was inserted. The terminal post was then passed through the grommet and the well surrounding the post, above the grommet, was filled with grease. Thereafter a protective washer was placed about the post to cover the well area and the grease held therein.
While this approach allowed the post to slip, the rubber grommet might lose its elasticity, permitting acid to flow upwardly along the post and between the post and the grommet, achieving proper fit between the post and grommet was a problem and the washer might be raised exposing the grease directly to dirt and other damaging conditions.
In an effort to overcome this problem we have discovered a way to create a seal that will allow some amount of relative movement between the cover and the terminal post without breaking the seal therebetween.